1. Field of the Invention
The present invention relates to a pneumatic tire in which a tread surface is provided with a groove portion including a main groove continuously extending in a tire circumferential direction, and a land portion including a rib or a block separated by the main groove.
2. Description of the Related Art
Conventionally, various ideas have been cast around in connection with a problem of an irregular wear generated on a tread surface. As the irregular wear mentioned above, there has been known, for example, a center wear in which a center region of the tread surface is worn in a comparatively early stage, and a shoulder wear in which a shoulder region is worn in a comparatively early stage. As a generation cause thereof, there can be listed up an uneven ground pressure balance of the tread surface based on a tread pattern and a tire shape. In other words, in the case where the ground pressures are greatly different between the center region and the shoulder region, a difference in wear amount tends to be generated between the regions, and the center wear and the shoulder wear are generated.
A pneumatic tire described in Japanese Unexamined Patent Publication No. H8-99505 is structured such that a land portion is separated into a land portion main body and a narrow land portion by a vertical narrow groove extending in a tire circumferential direction, and a suppression of an irregular wear is achieved by sacrificing a wear of the narrow land portion. The narrow land portion is provided in a region where a wear in an early stage is concerned, and it is possible to concentrate the wear by utilizing a low rigidity thereof. Accordingly, it is possible to reduce an amount of wear of the main body land portion in the region mentioned above, so that it is possible to achieve the uniform wear of the tread surface. However, in the structure mentioned above, since a rigidity of an edge portion (an end portion adjacent to the groove portion) becomes lowered in accordance with the concentration of the wear, a rigidity balance of the land portion is deteriorated, and there is a risk that the irregular wear is inversely generated.
A pneumatic tire described in Japanese Unexamined Patent Publication No. H4-218407 is structured such that a plurality of small holes are provided in an edge portion of a block, and depths of the small holes are made shallower as farther away from a groove in a circumferential direction. However, this pneumatic tire is structured so as to uniformize a ground pressure in whole the block, neither disclosing a structure for reducing a difference in amount of wear generated between the center region and the shoulder region, nor suppressing the irregular wear of the tread surface.